Right away, there seems to be a confusion about Billy Prior's mental health. This can be seen in two ways: first, he is clearly afflicted by PTSD, and the lack of external stimulation leaves him unimaginably paranoid, beyond what he can explain in language. This leaves him with an urge to return to the place where his psyche made sense, to the place where his mental damage still has clear references. He wants to go back to war—even if it means death. To him, death on the battlefield is better than the confusing hell of being in real life with the damage of war untreated in his mind.
The other way the confusion is seen is through sexuality. Although in the novel, he is constantly blocked from his fiancee by Ada, Sarah's mother, this mother can be seen as a protective symbol of the marriage. Although Sarah and Billy want to be together, there is reason to be cautious. He is not who he used to be, and when the condom breaks, the confusion is seen in Billy's strange response; he both wants a child with her and doesn't want a child with her. Then, the reader learns he has been experimenting with homosexuality with a military leader.
The experimentation of sexuality and gender role comes as a response to Billy's subjection to the hells of war. He connects better with other men who have suffered in similar ways to him, and although there is no reason to suspect he was bisexual before war, he is certainly bisexual after war. This is an easy symbol to misread; it does not mean that sexuality only works in this way! Rather, it means that, for Billy, war has brought him into a fuller understanding of his dark side, the shadow self that he rejects in polite company, but which is plain and obvious when his life is being threatened. The novel even ends with a portrait of his near-death awareness; he knows for sure that he will die after a bullet wound prevents his escape.
